I remember first playing EaW demo as well. The land battle was hard at first, but you will get the hang of it eventually. And it will become more simplistic.

Use the civilians to capture the other reinforcment posts and then land more troops fast and furiously. Use chewy to capture the AtAt and you'll win in no time. Also use a bombing run to take out the power generator so the laser towers wont work.

To reach the power generator you must go up the map through the right side and then enter the base from the back.

Once you get the AtAt and the power is out it is only a matter of mopping up the enemy.